Electrically heated ice-removing covering



2,487,65&

Nov. 8, 1949 A. M. LA RUE' ELECTRICALLY HEATED ICE-REMOVING COVERING Filed April 17, 1948 lnnuulcl/llax Patented Nov. 8, 1949 .ELECTRICALLY HEATED ICE-REMOVING COVERING Albert M. La Rue, Akron, Ohio, assignor to The B. F. Goodrich Company, New corporation of .NewYork York, N. Y., a

Application April 17, 1948, Serial No. 21,725

15 Claims.

The invention relates to electrically heated coverings for surfaces exposed to ice-forming conditions, especially leading edge surfaces of airfoils such, for example, as propeller blades, wings, and control surfaces.

For preventing the accumulation of ice upon the leading edge of an airfoil, it has been found advantageous to provide greater heat at the immediate leading edge region than that to the rearward or side regions of the covering. Expedients proposed heretofore to yobtain this result have not been entirely .satisfactory in View of the problems sometimes unavoidably introduced in the way of providing conveniently for the necessary electrical connections and providing the desired iiexibility and eve-n stretching in proper places to make the covering conformable to the compound curvature of the airfoil surface.

Objects of the invention are to provide for flexibility and stretchability in proper places of f ythe covering to facilitate conformingthe covering to -cuIved surfaces.; to provide for the electrical connections of the covering in which covering greater heat is effected at the immediate leading edge region than that to the rearward regions thereof; and to provide for fa close disposition of heating elements and uniformity of heating along gthe covering.

Other objects are to provide for ilexure of the covering about its longitudinal neutral axis of bending without buckling of the conductors, heating elements and other parts thereof; io provide for greater flexibility and stretchability of spaced-apart marginal portions `than that of a portion therebetween to facilitate conformance with the curved surface of the airfoil, especially at the root of a propeller blade; to provide for convenience of installation and for holding the installed covering in place throughout its extent;

.and to provide for thinness and durability of construction, convenience of manufacture and for effectiveness of operation.

. These and other objects and advantages of the invention .will be apparent from the following description.

n In the drawings which form a part of this specication and in which like numerals are employed to designate like parts throughout the same,

electrically heated coverings on a multi-blade aircraft propeller and constructed in accordance with and embodying the invention, parts being broken away,

Fig. 2 is a plan view from above of a covering as molded and before installation on the propeller blade, parts being broken away,

g Fig. 3 is a sectional view taken along line 3-3 of Fig. 2,

Fig. 4 is a plan view from above on an enlarged scale showing a portion of the covering at a conductor thereof shown in Fig. 2, parts being broken away, and

Fig. 5 is a view like Fig. 2 but showing a modified construction of the covering.

In the illustrative embodiment of the -invention shown in Figs. 1 to 4, inclusive, the covering has a body II) of resilient rubber, natural or synthetic, or other rubber-like material having electrical insulating, heat-resisting and abrasionresisting characteristics. Within the rubber body adjacent its outer surface there is provided a serpentine or looped arrangement of laterally disposed reaches of a plurality of flexible strip heating elements which may be resistance wires I I, I2 of the desired electrical resistance. For maximum flexure the wires may be of fine gauge and stranded form.

The rubber body I0 has embedded therein a pair of conductors I3, I 4, which may be of flexible, braided wire in vilat'strip form capable of stretching and shortening without objectionable buckling. The conductors extend longitudinally .of the covering in spaced-apart, substantially parallel relation one to another throughout the heating area of the covering. The conductors separate a leading edge or intermediate portion .l5 between the conductors, that may be disposed along and across the leading edge center-line, from `side portions I6, Il rearwardly thereof which extend laterally beyond the conductors toward opposite marginal edges I8, I9 of the covering.

The invention makes possible conveniently effecting a mode .of heat dissipation providing greater heating of one portion of the covering than that of another portion, which in the case of propeller blade coverings, for example, may be greater heating at the immediate leading region along the leading edge center-line of the blade than rearwardly thereof. Moreover, this result may be obtained with a determinate ratio between the portions of wattage dissipation per 45 unit area.

Fig. l is a front perspective view from above of '50 The looped wire arrangement shown in Fig. 2 provides greater heating of the leading edge or central portion I5 than that of the side portions IB, I1. The wire II extends laterally in the direction across .the conductors from the conductor I3 to which it has a first connection, across lthe portion I5 between `the conductors and into the side portion I'I and returns to the conductor I4 thereby providing in the side portion a loop having spaced-apart reaches 20, 20. The Wire II .continues from a reach 20 of the loop across the central portion I5 into the other side portion I6 Aand returns to the conductor I3 providing in the portion I6 a second loop having spaced-apart @0 reaches 2|, 2l- The wire lI then continues in a portion I6, I1 and five heating elements in the central portion I5, whereby the desired increased heating action at the central portion I5 is accomplished with lesser heating at the side portions I6, I1.

A second resistance wire I2 may be similarly disposed in the covering and in a manner so that end loops of adjacent Wires II, I2 have end portions of the Wires disposed within one another of said end loops. Since the spaces between end reaches 2U, 20 and 23, 23 of the wire II may be relatively Wider than those between the intermediate reaches 2|, 2I and 22, 22, this facilitates the rst connection of the wire I2 to the conductor I3 at a position between the reaches 23, 23 and less advanced than the second connection of the adjacent preceding element II, to permit close and substantially uniform spacing of the Wires in the portion I5 for providing Continuity of heating along the portion I5. Additional Wires Il, I2 are disposed in like manner throughout the entire heating area of the covering.

Thus, there is provided a plurality of heating elements disposed in succession along the conductors, each element extending laterally of the conductors and deviously from one conductor to the other and having a first connection with a conductor and a second connection with the other conductor at a position advanced along the conductors with respect to the rst connection, and the rst connection of each of a plurality of the elements being at a position less advanced along the conductors than the second connection of the adjacent preceding element. This makes possible a variety of arrangements of the heating elements while facilitating close spacing of the elements and uniformity of heating along the covering.

The wires II, I2 may pass over the conductor I3 and under the conductor I4 as shown especially in Figs. 2 and 3, the ends of the Wires being secured as by soldering to the under side of the conductors I3, I4. A continuous insulating strip 24, -24 of square-woven, cotton or glass fabric material friction coated with suitable rubber insulating material is disposed between the Wires and each conductor at the crossing positions Where contact is not desired, as shown especially in Fig. 4. A continuous strip or layer 25, 25 of suitable rubber material may be disposed between each insulating strip 24, 24v and its associated conductor I3, I4 for further insulating the wires from the conductor and for filling the interstices of the conductor with rubber by flow of the latter under vulcanization thereby avoiding objectionable air bubbles or pockets in the covering.

The rubber body I0 has, preferably, sheet reinforcements 26, 21 of square-Woven, bias-cut,

cotton fabric material friction coated with suitable rubber material, as shown especially in Fig. 3, overlying and underlying the heating means assembly comprising resistance Wires Il, I2 and conductors I3, I4 so that protective layers 28, 29

of the rubber body I Il overlie and underlie the reinforcements. The fabric reinforcements facilitate anchoring the Wires and conductors in position during manufacture of the covering for resisting localized displacement of such heating means assembly, especially under flow of the rubber upon vulcanization. The reinforcements also permit some stretching of the side portions I6, I1 When the covering is applied to the leading edge surface.

At its tip end, the covering may be provided with an end holding portion 30 of all-rubber construction projecting longitudinally beyond the ends of the conductors for facilitating installation of the covering upon, for example, each blade 3|, 32, 33 of an aircraft propeller 34. Although the holding portion 30 may be Wholly removed by a subsequent trimming operation, it has been found advantageous to utilize the holding portion 30 for many propeller blade applications. The portion 3D promotes holding the tip end of the covering in position on the blade under rotating conditions despite the loosening effect of centrifugal forces, and in addition also protects the tip of the blade itself against erosion and Wear due to hail, sleet, sand and other foreign material in the ambient air. 'Ihe construction facilitates balancing the propeller blade after installation of the covering on the blade by trimming the portion 30 as required.

At the root end of the covering, end portions of the spaced-apart conductors I3, I4 may extend first to a central position of the covering and then side-by-side in insulated relation to one another within a flat, lead-in strip 35 of rubber material, whereby the conductors may be connected to a suitable source of electrical energy.

In producing the covering, the protective layer 29 and the fabric reinforcement 421 may be superimposed and adhered together by a suitable rubber cement while uniformly supported in a substantially flat condition. The conductors and heating Wires are next adhesively anchored to the reinforcement in the disposition described hereinabove. One of the conductors, for example conductor I4, having the ends of the wires II, I2 soldered thereto is adhesively mounted on the fabric with the Wires extending across and beyond theiside heating portion I1; the rubber strip 25 and the fabric insulating strip 24 are next cemented down overlying the conductor.

Then the Wires are looped back and forth across the portions I5, I6, I1 and overlying the conductor I4 and strips 24, 25 until the last loop is reached. The other insulating strip 24 and rubber strip 25 and other conductor I3 are successively adhered in position overlying the wires II, I2 after which the last loop is completed and the other ends of the wires soldered to the conductor I3. The other reinforcement 26 and protective layer 28 are next cemented successively in place overlying the heating Wire-conductor assembly, the covering thus being in assembled relation in condition for vulcanization.

The fabric and rubber parts of the covering are desirably integrally united as by vulcanization under heat and pressure and may be molded in at form. For the molded condition, the side portions I6, I1 taper insection to thin marginal edges I8, I9, as shown especially in Fig. 3, for facilitating flexure and stretching of portions I6, I1 to conform with the curvature of the blade and for avoiding objectionable disturbance of the airflow across the blade.

The installation of ythe-covering in the-flat condition -upon the propeller blade `iis accomplished 'by flexing the covering according tothe longitudinal and lateral curvature of the leading edge and desirably adhering 'the covering thereto as Vby a rubber 'cement of the air-curing type, S0

that the central portion is disposed about the leading `edge center-line-with the :resilient protective layer '28 exposed Adirectly to the ambient air. 4'By virtue of 'the disposition .of the flat, braided conductors -I3, I4 along the -sides of --vthe central -portion l5 and andthe relatively greater l'thick- 'ness of the vportion I5, the `flexible covering has --alongthe center-line of the leading edge of the "blade This is advantageous to facilitate the de- ;sired uniformity of disposition of the central vportion I5 about the leading edge and the smooth yconformance without buckling of the side portions I6, I'I to the rearward areas of the'blade,

especially at the Vroot -of 'the latter Ywhere relatively'abrupt changes in blade contour occur.

This construction avoids a condition wherein conductors might stiffen the side or marginal portions obectionably against flexure and cause buckling of the same including the heating wires, especially at the root of the blade. 'The tapered -side or marginal portions I6, I`I ofthe covering Ill are relatively free to stretch and ex to the compound curvature of the blade surface and 'buckling of the heating wires imbedded in the vportions I6, I1 is avoided.

A further advantage of the arrangement of the conduct-ors I3. I4 at the sides of the central portion lies in the fact that inasmuch as these conductors may oder some resistance to the ow of electrical current and hence eiect a heating action along the margins of the central portion I5 supplementing the heating effected by the resistance wires in this portion, the elfective iceremoval at the leading edge is facilitated. The greater heating at the central portion I5 is advantageous in that it is in this portion where the ice tends to form in greater thickness thus requiring greater heat for removal, as compared to that at the side portions where the ice-deposit is thinner and hence less heat is required.

The chordwise extent of the heated area of the covering may vary from about to 100% of the chord of the blade, and the central portion I5 providing increased concentration of heat in the` leading edge region may extend back approximately 10% of the chord of the blade. Good reytral heating portion I5 and an overall heated area chord coverage of about Although the covering may, if desired, extend the full length of the'blade, it is preferable that the covering extend not less than the major portion of the length of the leading edge.

Since relatively greater erosion, abrasion and deterioration of the covering by the impact of foreign particles tends to occur at the radially outward region of the propeller, the heating wires or conductors or both in such region may, after extended use, become damaged or broken. The construction .advantageously facilitates cutting off the damaged tip-heating portion of the covering without effecting the heating action of the remainder thereof and Withoutremovingthe `entire covering 'from theblade thereby :increasing the service life and the safety of operation -of-thecovering.. *I

'The modified-construction 40 shown in Fig. 5 differs from that of the --covering AIlllin lthe lrespect of the number of loops of each resistance wire 4I, 42 between its connections to spacedapart conductors 43, 4'4 whereby a greater number of reaches of the Wire-are disposed in 'a cen- Itral portion A than those -in each side portion 46, 41 for-providing greater ,heat at the portion 45 "than that at the side portions. Each Wire 4l, 42 has a single 'loop having a pair of spacedapart reaches in each side portion 46, 4l as shown in Fig. 5. The covering 40 also includes inthe rubber material thereof suitable fabric reinforcements 48, 49 overlying and underlying the heating wire-conductor assembly.

Variations may be made without departing from the scope of the invention as it is defined =in the following-'claims l. Apparatus for .preventing the accumulation of ice upon a surface exposed to ice-forming conditions, said apparatus comprising a covering for said surface having electrical heating means therein .comprising a pair of spaced-apart conductors extending along the covering, the first of which conductors separates a region of said covering between said conductors from a region of said covering beyond lsaid iirst conductor, and a resistance element connected to the other conductor'and-extendinglaterally thereof across said region .between said conductors and into said region beyondsaid first conductor and returning to lsaid iirst conductor and connected therewith in a manner providing a greater number of reaches of said element in one of said regions of the covering as compared to the number of reaches of the element in the other region of said covering.

2. Apparatus for preventing the accumulation o'f ice'upon a surface exposed to ice-forming conditions, said apparatus comprising a covering for said surface having electrical heating means therein comprising a pair of spaced-apart conductors extending along the covering, the rst `of which conductors separates a region of said covering between said conductors from a region of said covering beyond said first conductor, and a resistance element connected to the other conductor yand extending laterally thereof across said region between said conductors and into said region beyond said first conductor and disposed 'in atleast one loop in the latter said region, said element returning to said first conductor and lconnected therewith in Aa manner providing a greater number of reaches of said element in one of said regions `of the covering than those in the other region of said covering.

v3. Apparatus-for preventing the accumulation of ice upon a surface exposed to ice-forming conditions, said apparatus V'comprising a covering for said surface having electrical heating means therein comprising a pair of spaced-apart conductors extending along the -covering and separating a region of said covering between said conductors from side regions of said covering beyond said conductors, and a resistance element connected to one of said conductors and extending laterally thereof across said region between said conductors and into one of said side regions and then backend forth in a'looped disposition across all said `regions of the coveringwith a loop in each of said side'regions and terminating at the other -conductor and .connected therewith in amanner yproviding a vgreater number of reaches loi said .element in said region between said conductors tas compared'to the numberof reaches ofthe element in each of said side regions of the cover- Apparatus for preventing the accumulation .of ice upon a surface exposed to ice-forming con- .ditions, said apparatus comprising a covering for vsaid surface having electrical heating means -therein comprising a pair of spaced-apart con- `ductors extending along the covering and separating a region of said covering between said conductors from side regions of said covering -beyond said conductors, and a plurality of resistance elements disposed along said conductors, `each element extending laterally of said conductors across all said regions and in a looped disposition in said side regions, end loops of adj ajcent elements having end portions of the elements disposed and connected to said conductors within one another of said end loops. Y 5. vAn electrically heated covering for preventing the accumulation of ice on the leading edge of -an airfoil, said covering comprising a body of resilient rubber-like material for said leading edge having in said body a pair of spaced-apart conductors extending along the covering, the rst of which conductors separates a leading edge portion of said covering between said conductors from a portion of said covering rearwardly of said rst conductor, said body having therein a resistance element connected to the other conductor of the pair and extending laterally thereof across said leading edge portion and into the rear portion of the covering and returning to said rst conductor and connected therewith in a manner providing a greater number of reaches of said element in one of said portions of the covering as compared to the number of reaches of the element in the other portion of said covering.

6. An electrically heated covering for preventing the accumulation of ice on the leading edge of an airfoil, said covering comprising a body of resilient rubber-like material for said leading edge having in said body a pair of spaced-apart conductors extending along the covering and separating a leading edge portion of said covering between said conductors from portions of said covering rearwardly of said conductors, said body Ahaving therein a resistance element connected to one of said conductors and extending laterally lthereof across said leading edge portion between said conductors and into one of the rear portions of the covering and then back and forth in a looped disposition across all said portions of the covering with a loop in each of said rear portions and terminating at the other conductor and connected therewith in a manner providing a greater number of reaches of said element in said leading edge portion than those in each of said rear portions of the covering.

7. An electrically heated shoe for a propeller -blade comprising a covering of resilient rubberlike material for the leading edge center-line por- .tion of the blade and portions thereof rearwardly of the center-line, said covering having therein a rst conductor at one side of the center-line portion of the covering, a second conductor in spacedapart relation to saidrst conductor at the other side of said center-line portion, said conductors separating said center-line portion from portions f of said covering to the rear thereof, and a resistance element connected to said second conductor and extending laterally thereof acrosssaid center- 8 line portion and into one of the rear portions of Vthe covering and then back and forth in a looped disposition across all said portions of the covering with a loop in each of said rear portions and terminating at said first conductor and connected therewith in a manner providing a greater number of reaches of said element in said center-line portion as compared to the number of reaches of the element in said rear portions of the covering. 8. An electrically heated shoe for a propeller blade comprising a covering of resilient rubberlike material for the leading edge center-line portion of the blade and portions thereof rearwardly of the center-line, said covering having therein a ilrst conductor at one side of the centerline portion of the covering, a second conductor in spaced-apart relation to said first conductor at the other side of said center-line portion, said conductors separating saidA center-line portion from portions of said covering to the rear there- ;of, and a resistance element connected to said second conductor and extending laterally thereof across said center-line portion and into one of the rear portions of the covering and then back and forth in a looped disposition across all said portions of the covering with a plurality of loops in each of said rear portions and returning to said first conductor and connected therewith in a manner providing a greater number of reaches of said element in said center-line portion than those in said rear portions of the covering.

9. An electrically heated shoe for a propeller blade comprising a covering of resilient rubberlike material for the leading edge center-line portion of the blade and portions thereof rearwardly of the center-line, said covering having therein a rst conductor at one side of the centerlne portion of the covering, a second conductor in spaced-apart relation to said first conductor at the other side of said center-line portion, said conductors separating said center-line portion from portions of the covering to the rear thereof, and a plurality of resistance elements in said covering disposed along said conductors, each element being connected to one of said conductors and extending laterally thereof across said center-line portion and into one of the rear portions of the covering and then back and forth in a looped disposition across all said portions With a loop in each of said rear portions and terminating at the other conductor and connected therewith in a manner providing a greater number of reaches of said element in said centerline portion as compared to the number of reaches of the element in each of said portions of the covering, said resistance element at its crossing positions wih respect to said conductors Abeing in overlying relation to one of said conductors and in underlying relation to the other conductor. 10. An electrically heated shoe for a propeller blade comprising a covering of resilient rubberlike material for the leading edge center-line portion of the blade and portions thereof rearwardly of the center-line, said covering having therein a pairof spaced-apart conductors at the sides of the leading edge center-line portion of the covering and separating said center-line portion from portions of the covering to the rear thereof, and a plurality of resistance elements in said covering disposed along said conductors, each element being connected to one of said conductors and extending laterally thereof across said center-line portion and into one of the rear portions of said covering and then back and forth in a looped disposition across all said portions with at least one loop in each of said rear portions and terminating at the other conductor and connected therewith in a manner providing a greater number of reaches of the element in said center-line portion than those in said rear portions of the covering, end loops of adjacent elements having end portions of the elements disposed and connected to said conductors within one another of said end loops, and each of said resistance elements at its crossing positions with respect to said conductors being in overlying relation to one of said conductors and in underlying relation to the other conductor.

1l. Apparatus for preventing the accumulation of ice upon a surface exposed to ice-forming conditions, said apparatus comprising a covering body of stretchable material for said surface having a pair of spaced-apart conductors anchored to said stretchable material and extending along the covering, and a plurality of flexible and nonstretchable electrical heating elements anchored to said stretchable material in succession along the conductors, each element extending laterally of said conductors and having a rst connection with a conductor and a second connection with the other conductor at a position advanced along said conductors with respect to said first connection, and the rst connection of each of a plurality of elements being at a position less advanced along said conductors than the second connection of the adjacent preceding element so that by virtue of such anchorage and disposition of the non-stretchable heating elements their heating effect is maintained substantially unchanged while accommodating iiexing and stretching of the covering in conforming it to the surface.

12. Apparatus for preventing the accumulation of ice upon a surface exposed to ice-forming conditions, said apparatus comprising a covering body of stretchable material for said surface having a pair of spaced-apart conductors anchored to said stretchable material and extending along the covering, and a plurality of flexible and nonstretchable electrical heating elements anchored to said stretchable material in succession along the conductors, each element extending laterally of said conductors and deviously from one conductor to the other and having a beginning end connected to a conductor and a terminating end connected to the other conductor at a position advanced along said conductors with respect to said beginning end, and the beginning ends of elements being connected to a conductor at positions less advanced along said conductors than the terminating ends of the adjacent preceding elements so that by virtue of such anchorage and disposition of the devious non-stretchable heating elements their heating eiect is maintained substantially unchanged While accommodating exing and stretching of the covering in conforming it to the surface.

13. Apparatus for preventing the accumulation of ice upon a surface exposed to ice-forming conditions, said apparatus comprising a covering for said surface having a pair of spaced-apart conductors extending along the covering, the rst of which conductors separates a region of said covering between said conductors from a region of said covering beyond said rst conductor, and a plurality of electrical heating elements disposed in succession along the conductors, each element extending from a conductor into said region beyond the said rst conductor and returning to the other conductor in a greater number of reaches in one of said regions than in the other region and along a devious path in one of said regions, each element having a rst connection with a conductor and a second connection with the other conductor at a position advanced along said conductors with respect to said first connection, and the first connection of each of a plurality of elements being at a position less advanced along said conductors than the second connection of the adjacent preceding element.

14. Apparatus for preventing the accumulation of ice upon a surface exposed to ice-forming conditions, said apparatus comprising a covering for said surface having a pair of spaced-apart conductors extending along the covering and separating a region of said covering between said conductors from side regions of said covering beyond said conductors, and a plurality of electrical heating elements disposed in succession along the conductors, each element extending laterally of said conductors across all said regions and in a looped disposition in said side regions with a greater number of reaches in the region between the conductors than in each of said side regions, each element having a rst connection with a conductor and a second connection with the other conductor at a position advanced along said conductors with respect to said first connection, and the first connection of each of a plurality of elements being at a position less advanced along said conductors than the second connection of the adjacent preceding element.

15. Apparatus for preventing the accumulation of ice upon a surface exposed to ice-forming conditions, said apparatus comprising a covering body of stretchable material for said surface having a pair of spaced-apart conductors anchored to said stretchable material and extending along the covering and separating a region of said covering between said conductors from side regions of said covering beyond said conductors, and a plurality of flexible and non-stretchable electrical heating elements anchored to said stretchable material in succession along the conductors, each element extending laterally across all said regions and in a looped disposition in said side regions with a greater number` of reaches in the region between the conductors than in each of said side regions, each element having a rst connection with a conductor and a second connection with the other conductor at a position advanced along said conductors with respect to said rst connection, and the first connection of each of a plurality of elements being at a position less advanced along said conductors than the second connection of the adjacent preceding element so that by virtue of such anchorage and disposition of the non-stretchable heating elements their heating eiect is maintained substantially unchanged While accommodating iiexing and stretching of the covering in conforming it to the surface.

ALBERT M. LA RUE.

REFERENCES CITED The following references are of record in the le of this patent: 

